The present invention relates generally to an electric motor and more particularly to a speed control therefor.
Electric motor speed controls are presently available in a number of forms and formats. A quite simple D.C. motor control includes, essentially, a potentiometer for varying the input motor voltage and thus the speed of the motor.
Another type of speed control includes a linear variable differential transformer ("LVDT"). This transformer is far more complex and far more expensive than the potentiometer-type control.
In an application involving several D.C. motors and several speed controls, and where the motors will run virtually continuously, the commercially available equipment fails to provide a cost-justifiable, effective, and long-lasting speed control. The potentiometer-type controls, which are often available directly from the motor manufacturer, have only a limited life expectancy, and thus the failure rate is high under constant motion conditions. Further, the potentiometer-type controls have a tendency to develop "dead spots", i.e., operational "dead spots" which cause the motor to stop.
Linear voltage differential transformers are simply too expensive for multi-control applications. These "LVDT's" usually have far more capability than is required in the simple, multi-control application, and consequently the per unit cost is often unjustifiable.